We've had the 8:15 slot a couple of times. One time we were seated at 8:05 and one time we were seated closer to 8:20. If you are seated at the earlier time, the characters are moving well, and you're not going too slowly with your food, you could be out right around 9. I think 9:05 is our avg time out when we've got the 8:05 slot.
You mention rope drop...not sure if you mean being out to see the Welcome Show, but I doubt that's going to be possible. I believe they're still letting guests in the park closer to 8:45 (part of preventing stampedes for A&E and SDMT), meaning the Welcome Show happens closer to 8:35 (a few min after). All in all, unless you will probably make it out between 9 and 9:20.